The present invention relates generally to heat engines, and more particularly to Sterling style heat engines.
A heat engine is a system that performs the conversion of hear or thermal energy to mechanical work. It does this by bringing a working fluid from a high temperature state to a lower temperature state. A heat “source” generates thermal energy that brings the working fluid to the high temperature state. The working fluid generates work in the body of the engine while transferring heat to the colder sink until it reaches a low temperature state. During this process some of the thermal energy is converted into work by exploiting the properties of the working fluid. The working substance can be any system with a non-zero heat capacity, but it usually is a gas or liquid. Heat engines operate by cyclic compression and expansion a working fluid at different temperature levels such that there is a net conversion of heat energy to mechanical work. A closed-cycle regenerative heat engine with a permanent working fluid is known as a Sterling engine and its inclusion of a regenerator differentiates it from other closed cycle hot air engines. The Sterling engine is noted for its high efficiency compared to steam engines, quiet operation, and the ease with which it can use almost any heat source. Like the steam engine, the Sterling engine is traditionally classified as an external combustion engine, as all heat transfers to and from the working fluid take place through a solid boundary of a heat exchanger, thus isolating the combustion process and any contaminants it may produce from the working parts of the engine. This contrasts with an internal combustion engine where heat input is by combustion of a fuel within the body of the working fluid.
In a Sterling engine, the regenerator is an internal heat exchanger and temporary heat store placed between the hot and cold spaces such that the working fluid passes through it first in one direction then the other. The design challenge for a Sterling engine regenerator is to provide sufficient heat transfer capacity without introducing too much additional internal volume or flow resistance. These inherent design conflicts are one of many factors which limit the efficiency of practical Sterling engines. Since the Sterling engine is a closed cycle, it contains a fixed mass of gas called the “working fluid”, most commonly air, hydrogen or helium. In normal operation, the engine is sealed and no gas enters or leaves the engine. No valves are required, unlike other types of piston engines. The Sterling engine, like most heat engines, cycles through four main processes: cooling, compression, heating and expansion. This is accomplished by moving the gas back and forth between hot and cold heat exchangers, often with a rengenerator between the heater and cooler. The hot heat exchanger is in thermal contact with an external heat source, such as a fuel burner, and the cold heat exchanger being in thermal contact with an external heat sink, such as air fins. A change in gas temperature will cause a corresponding change in gas pressure, while the motion of the piston causes the gas to be alternately expanded and compressed.
The drawbacks to the Sterling style heat engine are first is the heat exchanger and regenerator are position with the engine making it bulky and difficult to fit in small areas. Second is that for the size of the heat engine, there is less power than would be imaged due to the constraints of moving the working fluid.
An object of the present is to provide a heat engine that is an improvement on current designs of a Sterling type heat engine for sizing and power.